Based on the premise that the task of systematic theology is to promote an understanding of doctrines by relating different doctrines to one another, and in dialogue with the religious-cultural context, this article provides a systematic proposal for understanding the Roman Catholic doctrine that affirms the church as the universal sacrament of salvation. This doctrine will be clarified by relating it to the doctrine that interreligious dialogue is part of the Catholic Church’s evangelizing mission. The context for this understanding is one in which religious diversity is both a fact and often times, a problem. The reflections begin with a survey of several terms and relations that are central to the doctrines that are being discussed. Bernard Lonergan’s notion of mutual self-mediation is then explained and presented as a tool for both Christian and ecclesial self-understanding. Mark Heim’s so-called ‘theology of religious ends’ is appealed to as a concrete way for mutual self-mediation to be practiced, and Lonergan’s ecclesiologial suggestions allow the notion to be applied on an ecclesial level.